1. Technical Field of the Invention
The present invention relates to the construction of a contact probe for use with a surface roughness meter, a profile measuring machine, or a three-dimensional measuring machine, and particularly to a profile measuring apparatus for measuring the shape of a cross-section of a scroll compressor for an air-conditioner, an outer diameter of a video tape recorder cylinder, the precision of a cylindrical body, the degree of concentricity, an inner diameter of a bore, the shape of a cross-section of a central aperture, the straightness of a leading distance (e.g. less than 1 micrometer on a tape guide for compatibility of VTR tapes), and so on without damaging the surfaces to be measured under a lower pressure at a high speed and with high accuracy in the order of 0.1 to 0.01 .mu.m.
2. Description of Related Art
A probe used for a surface roughness meter, a profile measuring machine, or a three-dimensional measuring machine may be selected from a contact probe, an interatomic force probe, an optical probe, a static capacitance sensor, and other applicable types. Neither the optical probe nor the static capacitance sensor are capable of measuring a side wall of a very small bore or of a minute step which is less than 0.1 mm such as a lead, and both are unfavorably used measurement of profile or roughness to as a high precision level as below 1 .mu.m.
The contact probe produces a considerable rate of pressure during measurement and may damage the surfaces to be measured. A conventional type of the contact probe is equipped with an operating transformer. As such an operating transformer includes a magnet or magnetic core, it adds an extra weight to the moving part of the probe. Therefore, improvement of the response speed of the probe results in increasing the contact pressure during measurement. Even so, the conventional contact probe remains as low in the response speed as about 10 Hz.
One of the interatomic force dedicated probes is disclosed in Japanese Published Unexamined Patent Application 6-265340, which is lower in the contact pressure than the contact probe thus giving little opportunity to damage the surfaces being measured. If a stylus is made of a 0.5 mm radius ball of ruby and the contact pressure is less than 0.2 g, a repulsive force is developed in an energy gap between the stylus and the measuring surface by movements of tunnel electrons. Hence, the interatomic force probe is termed after this effect. The interatomic force probe disclosed in 6-265340 is however designed for measuring the profile of a flat or lens surface from above and its usage is limited.
A profile measuring apparatus disclosed in Japanese Published Unexamined Patent Application 6-160075 is designed for measurement of the profile of scroll blades and can be sed for a wider range of application. The apparatus has a stylus mounted to a leaf spring 12 and illuminated from behind. Since a mirror and its holder have to be located very close to the stylus, the entire construction is relatively intricate, and it is almost impossible to set the stylus within an aperture of 2 mm diameter.
As for a video tape recorder cylinder, it usually comprises an upper driving cylinder and a lower stationary cylinder. The lower cylinder has such a shape where the measurement is made on the diameter of a center bore, external diameter, surface roughness, straightness and height of a lead portion, parallelism between the upper and lower surfaces, verticalness of the lower surface to the bore or outer wall, concentricity and cylindrical degree of the bore and outer wall and bore, size of a bulged portion for eliminating tape running noise, and so on. A total of 26 points of measurement are necessary for the upper and lower cylinders. While it is possible to separately measure the upper surface, lower surface, outer side surface, and inner side surface of a cylindrical member such as a video tape recorder cylinder, the verticalness of the lower surface to the side surface of a bore in the cylindrical body cannot be obtained. In a prior art method, the measurement of those points has been carried out using five to six separate measuring apparatuses. However, if the cylindrical body or object to be measured is unloaded from one measuring apparatus and re-loaded to another, its orientation will change thus rarely permitting the measurement with submicron precision.
It is nevertheless essential to measure profiles of a digital video tape recorder in the order of 0.1 .mu.m as compared with 1 .mu.m in an analog video tape recorder.
Accordingly, it is desired to provide a profile measuring apparatus having a novel probe with such capacities as described below.
1. The probe is capable of measuring such objects as a cross-section of a small aperture and of a step of less than 0.1 mm on the surface of a lead portion of a video tape recorder cylinder with high accuracy at a high speed, which have not been the targets of a known interatomic force probe, without producing errors of measurement even when the measuring surface is tilted or the stylus generates friction.
2. An arm having a stylus at a distal end and a spring at a proximal end is provided, the inclination of which is measured at a high level of response and with high precision.
3. A laser beam is precisely directed to a small mirror for detecting tilting angles of the arm.
4. The contact pressure of the stylus is minimized in order to avoid damage to the measuring surfaces, to retard its wearing, and to eliminate measurement errors caused by deflection of its arm, as well as the weight of the stylus arm is reduced. This is because a large weight of the moving part of the arm will cause decrease in response acceleration speed, resulting in decrease in measuring speed, since the response acceleration speed A of the probe is expressed by A=contact pressure/weight of the movable part.
5. The probe is so constructed that when an excessive contact pressure is exerted on the stylus due to an erroneous operation, the probe retracts and is prevented from physical fracture.
6. Similarly, when a stress of an abrupt impact is applied to the stylus, it retracts and is prevented from physical fracture.
7. Since the data of measurements from the probe falls in a narrow range of less than 1 mm which is equivalent to the movable range of the probe, the apparatus is so constructed to obtain coordinates of the measuring points from a wider measuring area.
8. The measurement of profiles with the probe is carried out continuously and two- or three-dimensionally by scanning throughout the wider measuring area under substantially a constant rate of the contact pressure.
9. The measurement of profiles such as roundness with the probe is carried out by using a polar coordinate system as well as an orthogonal coordinate system.
10. The measurement is carried out for determining the thickness and both the rough and fine profiles of objects.
11. The measurement of profiles is carried out with high accuracy in the order of 0.01 .mu.m in a coordinate system of the measuring points without being subject to the influence of poor straightness and pitching, yawing, and rolling motions of the stages.
12. The measurement of the verticalness of the upper or lower surface to the side surface as in a video tape recorder cylinder is carried out with high accuracy in the order of 0.01 .mu.m without loading/unloading the object more than once.